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I’ve been running Ubuntu 9.10 on my dynamips box for sometime and it’s worked perfectly with my 4 quad NICs.

Last week I stupidly decided to upgrade my distro to 11.10. All looked fine. Dynamips still worked and everything looked okay.

However I was having some problems. Whenever I had a emulated router runs tags on a port, it refused to properly speak to a trunked switch port. CDP still worked, but nothing else. After hours of troubleshooting I knew nothing was wrong with my configs. The only recent change was the install.

So I reinstalled 9.10, and not a single problem again.

This has nothing to do with MTU size, as a ping packet and an ARP packet have tiny payloads. I probably could’ve figured out what the problem was eventually, but it was eating into my study time. Reinstalling only took about 40 minutes and I was back in action.

The only problem with reinstalling is that Ubuntu changed the order of all my NICs. As my dynamips .net file maps certain router ports to certain breakout ports it completely screwed this up. I spent another hour sorting them out. This is my NIC file attached. Don’t use this yourself as your environment will be different of course.

Moral of the story. If you have a working system, don’t mess with it as you’re just wasting valuable time!